Percutaneous transluminal coronary angioplasty (PTCA) is often used to reduce arterial build-up of cholesterol fats or atherosclerotic plaque in coronary arteries. Typically a guidewire is inserted into an incision in an artery and is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the guidewire and a balloon catheter advanced within the guiding catheter over the guidewire. The balloon at the distal end of the catheter is inflated causing the site of the stenosis to widen. While the stenosis or occlusion is greatly reduced, many patients experience a reoccurrence of the stenosis over a relatively short period. Researchers have found that angioplasty or placement of a stent in the area of the stenosis irritates the blood vessel causing rapid reproduction of the inner layer of blood vessel cells and restenosis through a mechanism called hyperplasia. It has been found that irradiating the blood vessel walls at the point of the stenosis will reduce or prevent hyperplasia. Precise control over the amount of radiation is important, since insufficient radiation will not prevent hyperplasia and excessive radiation can damage the blood vessel.
For other diagnostic or treatment purposes, it is also often desirable to introduce a small radiation source into a body vessel such as a coronary artery. Simply inserting a wire with a source secured in the wire at or near the distal end is effective in some cases. However, the wire will tend to lie along one side of the vessel, so that the near side receives significantly more radiation than the opposite, distant side. The near side could receive excessive, damaging, radiation exposure before the opposite side received the desired dose. Such a non-centering, wire-carried, radiation source is shown by Dake et al. in U.S. Pat. No. 5,199,939 and Bradshaw in U.S. Pat. No. 5,643,171. Therefore, it would be highly desirable to provide a radiation delivery system that would assure that the source is centered in the vessel.
Zoumboulis, in U.S. Pat. No. 3,324,847, describes a catheter having a spherical inflatable chamber adjacent the catheter distal end. A fluid containing a radioactive material such as radioactive iodine is pumped into the chamber, inflating the chamber and treating the vessel walls with ionizing radiation. The chamber will stop blood flow, so can be inflated for only a short period. Further, precisely controlling radiation exposure and fully draining the chamber to end treatment are very difficult.
A wire carrying a radioactive source could be inserted through a catheter lumen to the balloon location. The balloon would approximately center the source in the artery. However, since many guide wires extend mainly alongside the balloon catheter and balloons generally expand somewhat unevenly, the source would not be precisely centered. Further, irradiating a segment of an artery or the like generally requires some time, typically from about 3 to 45 minutes. Since a conventional angioplasty balloon substantially shuts off blood flow through the artery, treatment can be conducted for only short periods before damage from lack of blood flow becomes significant.
Liprie, in international patent application publication number WO95/26681 describes a device for treating a vessel occlusion with radiation in which a ribbed balloon catheter is inserted into a body vessel and inflated to provide perfusion between the ribs and a wire carrying a radiation source is inserted into a lumen extending into the balloon area. This positions the radiation source generally near the center of the vessel. However, as disclosed, the lumen has a much greater inside diameter than the outside diameter of the source wire, so that the source will generally be off center, in contact with the lumen wall. This will result in uneven irradiation of the vessel wall on opposite sides.
Other ribbed arrangements, using a double spiral rib or circumferential ribs are disclosed by Bradshaw et al. in U.S. Pat. No. 5,643,171 for centering a treatment lumen in a body vessel. While useful, the lobes may not provide precise centering, especially if the treatment wire is not a good fit in the lumen.
Teirstein in U.S. Pat. No. 5,540,659 describes a series of centering wire loops for centering a wire-carried radiation source in a body vessel. The generally oval shape of the wire loops and the complexity of inserting and removing the loop device make this arrangement less than fully effective. Teirstein also shows in his FIGS. 5 and 6 an embodiment using flexible wires that can be expanded away from a central catheter. However, the use of a single set of wires extending from the distal to proximal ends of the treatment zone will tend to allow the catheter to tilt relative to the wires. Also this system does not allow the use of multiple sets of expansion wires that could be opened independently.
A series of approximately spherical balloons are used to center a radiation source in the arrangement of Verin et al. as disclosed in European patent application number 94109858.4. Although the source is centered in the vessel, lack of perfusion of blood past the site would permit only very short treatment times.
Thus, there is a continuing need for improved devices for carrying a radiation source to a desired site along a body vessel that can be easily and accurately inserted into and removed from even very small vessels and which accurately center the source in the vessel while permitting effective perfusion so that treatment can be conducted over reasonably long periods.